As noted in 4db5bfb1757a3a4a3211c5985195a95f8994c644, I've switched postfix to only use ip4, I need to take some time to understand ip6 and postfix and figure out everything that needs to be done to make it work.
This should fix these errors in the logs:
connect to smtp.example.com[NNNN:NNNN:NNNN:NNN::NN]:25: Network is unreachable
As noted in 4db5bfb1757a3a4a3211c5985195a95f8994c644, I've switched postfix to only use ip4, I need to take some time to understand ip6 and postfix and figure out everything that needs to be done to make it work.
This should fix these errors in the logs:
https://www.digitalocean.com/community/questions/can-not-send-any-email-from-postfix